1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How can I get rid of air buildup in a siphon system

  1. May 20, 2015 #1
    I have been trying to control the water level in a water hole that I have using a siphon system. I have a 1.5 inch hose that is submersed in the upper water hole and the hose travels slightly up hill for a 100 feet then goes slightly down hill for the other 100 feet into a large barrel of water which just overflows during the siphon process. The water level of the top of the barrel is the level I want to achieve in the upper water hole. Everything works very well for about 6-7 hours of siphon but eventually small amounts of air bubbles build up into large air pockets and siphon is eventually lost. I can't really change where the hose is. How can I release this eventual build up of air automatically without losing the siphon. Is there some kind of valve? Or some trick that can be used to stop the build up of air from travelling down the hose? I have been reading that there are various reasons why the gas build up is happening. I can't really change that but I am hoping of a way to dispose of the gas? Any help would be greatly appreciated. Thanks
     
  2. jcsd
  3. May 22, 2015 #2

    Baluncore

    User Avatar
    Science Advisor

    Welcome to PF.
    This is a problem with ground water that contains dissolved gasses. The problem is greatest where the siphon has the greatest possible height and so pressure reduction. It is not really the distance the siphon travels diagonally but the height it lifts water that determines the depression at the top of the siphon.
    There are many solutions available.

    You could attach a large reservoir to the top of the siphon. Low pressure gas would gradually collect there until you turn off the normally open bottom valve and refill the reservoir with water through the normally closed top valve. Reservoir size would need to be large for a siphon with a big height difference. That gas might be worth collecting if it is something like methane.

    A small positive displacement vacuum pump could operate to very slowly draw low pressure gas from the top of the siphon. It could be hand, solar or wind powered.

    By using a bundle of fine tubes rather than one big pipe, gas bubbles coming out of solution towards the top of the siphon would remain entrained in the liquid flow until they redissolved or bubbled out at the end of the siphon.

    Keep the siphon tube cool and out of the sun. Gasses are more soluble in water at low temperatures than high. The water from underground will probably be cool.

    If the gas is mostly CO2 then you might consider a chemical absorber like used in a scuba re-breather. That could be expensive. http://en.wikipedia.org/wiki/Soda_lime
     
  4. May 22, 2015 #3
    Thanks so much for the reply Baluncore. I will try to use one or more of these suggestions to rid of this problem.
     
  5. May 23, 2015 #4

    OCR

    User Avatar

    Yes... very good advice from Baluncore.

    Also, if you can, check for any pin holes in the hose...

    You have probably read this ... but maybe other people haven't.

    According to the Talk page, the article could be a bit better... siphons due seem to be somewhat complicated.

    Look at the View history page too... I think I made the last edit... :approve: ... Lol.
     
    Last edited: May 23, 2015
  6. May 26, 2015 #5
    we have decided to install a small battery operated vacuum pump that only turns on when a certain amount of gas is gathered at the top of the siphon. Will let you know how it works
     
  7. Jul 7, 2015 #6
    So I am still fighting with gasses collecting in this siphon system. We added a container at the highest point of the siphon system with a shut off valve. The container was filled with water. Our idea was to for the container to catch all the gases and replacing the water in the container with the gas. The shutoff valve would allow us to remove the container to remove gas and refill with water. If this would have worked we would have used a larger container so that it wouldn't have to be refilled as often.
    We primed the siphon and once it was working we opened the valve. To our surprise the water was sucked out of the container so fast that it flattened the container. Fail! Our thought now is to get a container that won't collapse. Any other suggestions? Is there some kind of auto air bleeder or degassing valve that would work in a siphon system? It certainly would make this a lot more simple to achieve. We can get the siphon to work for a few hours and then the gasses build up enough that it losses the siphon. Getting rid of these gassed is proving to be a lot more difficult that I had thought.
     
  8. Jul 7, 2015 #7

    Baluncore

    User Avatar
    Science Advisor

    You will need a transparent vertical canister between two ball valves, all mounted on a T connector at the highest point on the siphon tube.

    Repeat the following cycle whenever you need to remove low pressure gas from the top of the syphon tube.
    1. Close the bottom valve.
    2. Open the top valve, (expect it to suck in some air).
    3. Fill canister with water through the top valve to displace gas.
    4. Close the top valve.
    5. Open the bottom valve so gas can again rise into the canister as it appears in the siphon.

    The bigger the canister, the less often you need to flood it again.
    The greater the siphon head the greater will be the partial vacuum, so a greater volume canister will be needed to remove the same mass of gas.
     
  9. Jul 7, 2015 #8

    russ_watters

    User Avatar

    Staff: Mentor

    A bleeder valve won't work because as you found, the system is negatively pressurized at the top. You need a rigid container, capable of handling a pretty healthy vacuum without collapsing. Your (Baluncore's) solution was a good one, you just need a stronger container.
     
  10. Jul 8, 2015 #9

    anorlunda

    Staff: Mentor

    Baluncore's suggestion to use a bundle of small tubes, is very clever indeed. It would make a fun project for students to find out how small the tubes have to be.
     
  11. Aug 2, 2015 #10
    this is what we tried so far. Seems to work so we need to get a larger canister now. I would like to try a collection of smaller tubes though. I just have so much money invested in this right now. 20150719_094353_resized.jpg 20150719_094459_resized_1.jpg
     
  12. Nov 5, 2016 #11
    Foot valve on water source side pressure release valve on top of the collector, 100ft header pump on barrel side, with timer to force out the air.
     
  13. Nov 8, 2016 #12
    A couple of quick questions. 1) what sort of acceptable range in the receiving vessel. 2) What sort of initial and overall topographical head are you dealing with? It seams as if a conventional dosing siphon would maintain your levels. This type siphon resets itself with each dose and as a byproduct it clears the dissolved gasses when the transport purges.
     
  14. Nov 9, 2016 #13

    anorlunda

    Staff: Mentor

    Wow, I learn something every day on PF. I never heard of a dosing siphon, so I looked it up. I found this very interesting page. Very clever.

    http://www.siphons.com/how-siphons-work.html
     
  15. Nov 9, 2016 #14
    There are a few simple considerations if a Dosing siphon is to be used. First is the Topographical head from dose tank to receiving tank. If it is consistently negative then it is quite easy. If it has a positive component along the run it can be done but with special consideration. They will not develop enough pressure to overcome any positive topographical head.
    A second consideration is that the void volume of the initial transport pipe needs to be sufficient to dissipate the air bubble. If pipe size due to outside issues is going to be restrictive there would need to be further consideration.
    Last is the dose volume. A dosing siphon is easy to calculate in that it triggers at a predictable height above the bell and it will brake at a predictable height below the bell. This distance (for instance in inches) multiplied by the Gallons per inch of the tank you are using will tell you the overall dose volume. One can by varying relationships change the dose volume as required. The only restriction being the initial surge going into the primary pipe.

    Advantages for you is: 1)That they operate strictly by gravity and without external applied power. 2)They are self priming at each dose. 3) As the transport drains out each cycle and the new cycle flushes the pipe, dissolved or suspended gasses do not affect them by virtue of not accumulating.
    If this of interest to your application we can continue towards a solution. If not you still learned a cool new tool.
     
  16. May 22, 2017 #15
    I'm still having issues with this siphon system. I would be interested in trying a Dosing siphon but I don't know much about them and not sure if it would push the water uphill for a hundred feet. On another note, if I used a 1 1/2" initial source hose up to the crest and then used a 2" hose downhill to the lower barrel would this created a faster flow on 1 1/2" hose thus making the dissolved gases flow out instead of accumulating at the crest?
     
  17. May 22, 2017 #16
    It still is a question of overall head. The length of pipe makes a bit of difference that we can address in a few. From the high point in your feed tank to the high point of the transport line the height of the lift determines the depression in pressure. This would be what is causing the water to flow up hill and generally what could be considered to be causing the dissolved gasses to come out of solution. (1) we would need to know what that lift height is not the lateral run of the pipe.
    Now speaking to the length of transport and your suggestion for a pipe change. What you are suggesting would have a negative affect on the function. The pictures you shared show what looks like a PVC spa hose. There are several variations that are loosely the same as schedule 40 rigid. The outside diameter is the same so glued fittings still work. Without knowing the exact hose I need to shift to generalities.
    For all plumbing systems the positive or negative pressure is generated by the topographical head not the physical size of the transport. A water column that is 33.6 feet in height in a 1/2 " pipe will generate exactly 1 atmosphere of pressure. A water column of the same height in a 2" pipe will generate exactly the same pressure.
    There is to be considered that a larger pipe has more square inches for the pressure to act against. However this also affects the volume. Your 1 1/2" hose will hold between 11.5 and 12.9 gallons per 100' of pipe. Thus anything entering (including gasses) the system must travel for whatever amount of time it takes for the requisite volume to transit. When you step up to 2" hose the volume is 17.9 to 20.3 gallons per 100'. With that increase in area the flow rate (which is all drawing through the same orifice) is slower. An interruption in flow such as a bubble will flow quickly up the hill but slowly down which is where it will create the greatest disruption.
    Interestingly enough the siphons, even the ones that were accidental in nature, that are the most efficient (and thus the hardest to prevent) are the ones that are in a smaller tubes. With the flow speed up they are constantly flushing themselves of violations. Also on a uniform hill ( say 10% up gradient and 10% down gradient) the uniform piping allows for a net 0 when disrupted.
    If you do decide to go with a dosing siphon you will find that it is critical that the initial piping, which is right after the siphon be sufficiently large to allow the entire air bubble to evacuate allowing manifold fill for the rest of the system.
     
  18. May 23, 2017 #17

    Baluncore

    User Avatar
    Science Advisor

    There are a couple of things that I would check.
    Firstly; if the well recharge rate is low, then the water level in the well will fall as water is removed. At some point air will enter the siphon tube, how is that prevented. What regulates the flow rate from the well so as to keep sufficient water in the well.
    Secondly; the gas that accumulates in the high reservoir is at a low absolute pressure. It is therefore very difficult to pump it out efficiently.It would be better to keep it as small bubbles in a fast flow. That suggests a smaller pipe would be better.
     
  19. May 24, 2017 #18
    The recharge rate right now is quite fast..it is a ditch that surrounds a couple of acres and water runs in at one end. We had a large hole dug in the ditch at the siphon intake with a large garbage can which has the end of the hose in it to keep debris out and lets water in through holes. The hose travels approximately 100 feet to the crest then gradually downward another 100 feet to a barrel full of water. The top of the barrel is about two feet lower than the intake hose. If the water in the ditch drops two feet the water level in the ditch and the lower barrel will be at the same level and siphon should stop. If water then increases in the ditch the siphon should just keep going since both ends of the hose is still submerged. This was our hope anyway. We never get that far along because I assume the dissolved gases is breaking the siphon eventually( in less than 12 hours). Water runs out of the barrel quite fast in the beginning. It is surprising to me that it ever stops. If we just left the hose on the ground instead of the barrel in would eventually drain the ditch if not for dissolved gasses but we don't want it drained otherwise siphon will need to be reprimed after a rain. I live 2 hours away. Sounds like our only solution is a few smaller hoses. Would raising the crest higher make a faster flow? What size small hose would be ideal for keeping air bubbles flowing?
     
  20. May 24, 2017 #19

    Baluncore

    User Avatar
    Science Advisor

    Raising the crest would be a disaster. You are already too close to the height limit which is why the water is close to, or is “boiling” at environment temperature and releasing all the dissolved gasses.
    The height limit of a siphon will depend on the minimum atmospheric pressure when there is a low pressure system and the higher density of water at low tube temperatures. It is lower still for salty water which has a higher density.

    One or several smaller tubes will work only while the water keeps moving, but thin tubes have much greater flow resistance so they will each carry much less water. Keep the thick riser tube, but replace only the downhill section with a 6mm = ¼ inch nylon pneumatic line which will be low cost and has cheap fittings. Experiment; when you find a size that pulls the gas through the system, work out the flow you need and duplicate the downhill run with several parallel lines.

    Relying on the height to stop the siphon as inlet falls is risky as it means the pressure difference is close to zero and so the fluid flow is very slow. That slow flow will not remove gas bubbles through small tubes.
     
  21. May 24, 2017 #20
    You still seem to be missing the point. It is the relative height of the inlet and the outlet that generates the siphon. If there is a crest in the center that is of negligible effect other than being a cause for priming the siphon. I am assuming that the crest is not 100 feet above the inlet tank. 100 feet of lateral distance is of little consequence.
    As to the size of hose that would be best. How much water do you need to transfer and at what rate? Also we need to know the relative height difference between inlet and outlet. This determines the pressure that is available for use. The hose would be the orifice and then the flow rate can be calculated with the data using the orifice flow formula or more accurate a calculation involving a Reynolds number if available for the hose that is in use.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: How can I get rid of air buildup in a siphon system
Loading...